The long-term goal is to characterize learning-dependent changes in sensory coding strategies in early somatosensory cortices. Ultimately, we aim to characterize such changes both at a phenomenological and mechanistic level. The present research focuses on determining whether such plasticity exists. Specifically, we will test the hypothesis that learning a whisker-dependent sensory discrimination task increases the accuracy of the sensory code in neuronal ensembles in the first and second somatosensory cortices (SI and Sll) of the rat. We have previously quantified the rat's ability to behaviorally discriminate between a narrow and wide aperture using its whiskers. We will first create a version of this task in which the rats will discriminate between two aperture width categories ('narrow'and 'wide'), each of which contains two widths. We will design the stimulus categories so that the distance between widths within a category is identical to the minimum distance between widths across categories. After designing the task, we will implant multielectrode arrays in SI and Sll and record from neuronal populations while rats learn the task. We predict that SI and Sll will discriminate the between-class widths (i.e., those behaviorally discriminated) better than within-class widths (i.e., those which the rat does not behaviorally discriminate) that are separated by the same physical distance. We will quantify discrimination with percent correct of a classifier that estimates aperture width based on the neural response. There are considerable potential clinical rewards for characterizing the mechanisms of cortical plasticity. If early sensory cortices adapt their coding strategies via behavioral training, this would offer great hope for the development of neuroprosthetics in patients with peripheral nerve damage, suggest behavioral paradigms for retraining those with minor sensory impairments (e.g., dyslexics), and suggest potential pharmacological manipulations to maximize the effectiveness of such treatments. Because of the ease with which rats learn whisker-dependent behavioral tasks, and the relative simplicity of the cortical representation of whisker stimuli, the rat whisker system is an ideal model system for examining such phenomena.